This application claims the priority of German application 198 65 774.4, filed Dec. 3, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a bearing arrangement for spindles in spinning and twisting machines comprising a rotatably supported shaft as well as a bearing housing, a neck bearing, a step bearing and a radially movable step bearing tube, which is arranged in an oil bath, whereby the diameter of the shaft is smaller at the step bearing tube than at the neck bearing.
Bearing arrangements of this type are well known in practice and are described, for example, in the brochure Suessen-Novibra Technical Information SCT.6114 ND. The shaft of standard spindles in the short staple field of practically all makes has a diameter at the neck bearing of approximately 6.8 mm and at the step bearing a diameter of approximately 4.5 mm, at a distance from the center of the neck bearing to the step bearing of 100 mm. These standard dimensions have become established over decades in practice as a presumed optimum. They take into account the fact that the shaft of the spindles must, in the area of the step bearing, be able to move radially to a certain degree, and that in particular the surface pressure at the step bearing must be under control.
For the smooth running of the spindle, the sliding bearing clearance in the step bearing is of great importance. Indeed, it would be desirable to reduce the bearing clearance. With the today standard spindle speeds of 22,000 rpm and more, a reduction in the bearing clearance leads however to an overheating of the step bearing, whereby small bubbles can form in the oil bath and thus lead to an occasional tearing off of the lubricating film.
It is an object of the present invention to improve the above mentioned bearing arrangement in such a way that a smaller bearing clearance than previously known is possible in the step bearing.
This object has been achieved in accordance with the present invention in that the diameter of the shaft at the step bearing measures at the most 0.6 times the diameter of the neck bearing.
By means of reducing the diameter of the shaft at the step bearing, the circumferential speed of the shaft at this point is reduced. Surprisingly, it has been shown that with this measure, bubble formation at the critical point can be avoided. The absolute bearing clearance can hereby be reduced in the desired way, which in turn leads to silenter running of the spindle. Advantageously, the difference in diameter between the shaft and the step bearing tube now measures 0.015 to 0.035 mm, at a diameter of the shaft of approximately 3 to 3.5 mm at this point.
Surprisingly, it has been established that, by applying the above mentioned measure, in addition the required power for the drive is reduced. A reduction of approximately 1 watt per spindle is possible.
In the case of lower spindle speeds, when the hydrodynamic pressure does not take up the bearing load at the step bearing completely, that is, the step bearing acts in the mixed friction area, further improvements of the spindle running can then be recorded when, between the shaft and the step bearing, a particularly narrow bearing gap is created in that the shaft at the step bearing tube is slightly spherical in form. As the shaft has to be ground in any case with a special grinding wheel in this area, the spherical grinding does not lead to a cost increase.
These and further objects, features and advantages of the present invention will become more readily apparent from the following detailed description of an embodiment of the invention.